Feedback from EMG Zakk Wylde set

So I have a SV 2x12 and an Epiphone Les Paul Ultra with a ZAKK Wylde EMG set installed. Whenever playing not loud I think I have the channel volume up all the way if not just more than halfway and the Master at what would be about 9 o'clock, so not that high. When ever playing if i palm mute something, lets just say, Say I - by Creed, the interlude where all Tremonti does is palmmute, I get feedback. A high pitched Feedback coming from the amp....any suggestions on what might be causing this? To much gain?